It requires a bit of knowledge and a commitment to managing the deploy, but: disable write permissions for the web user to the WordPress directory (excluding the upload folder), whitelist endpoints in nginx/apache, set up IP whitelists for /wp-admin/, minimize plugin usage.
This is going to reduce the user-friendliness of the WordPress install, but it's going to immediately increase the security by leaps and bounds. If you can't exploit plugins, can't access the admin pages, can't modify PHP files, and can't hit exotic endpoints, it's much harder to compromise WordPress.